Variation in secondary metabolites of Daphne mucronata Royle (Thymelaeaceae) by climatic factors and ontogenetic stages

Abstract

This study investigated the effects of specific climatic factors longitude, latitude, altitude, temperature, and precipitation on the secondary metabolites present in different organs of Daphne mucronata Royle across nine regions in Iran. Iran's diverse physiography gives rise to a wide spectrum of climatic conditions, ranging from arid and hyper-arid deserts on the central plateau to humid subtropical regions along the Caspian coast and cold, mountainous climates in the Alborz and Zagros ranges. This significant climatic variation makes the study of its influence on medicinal plants paramount. Secondary metabolites in various plant organs exhibited variable responses to the climatic factors. The highest phenolic content (1780.51 ± 0.23 mg/100 g DW) was recorded in leaves from the Shekarak region, whereas fruits from Dalin showed the lowest content (557.39 ± 0.7 mg/100 g DW). Total flavonoid content was highest in leaves from Margun (218.3 ± 0.57 mg/100 g DW) and lowest in fruits from Aspas (0.076 ± 0.02 mg/100 g DW). The highest levels of flavones and flavonols were found in leaves from Dalin (29.42 ± 1.03 mg/100 g DW) and Dejkord (25.06 ± 1.36 mg/100 g DW), with no significant difference between these two regions; fruits from Dalin exhibited the lowest content (3.005 ± 1.71 mg/100 g DW). Antioxidant activity was highest and consistent in flowers and fruits across all regions (95.23 ± 0.36 %), but it was lowest in leaves from Kakan (81.37 ± 1.12 %). Gallic acid concentration reached its maximum in leaves from Dalin (2350.87 mg/100 g DW) and its minimum in fruits from Margun (630.23 mg/100 g DW); leaves consistently contained higher gallic acid levels than flowers or fruits. Furthermore, total flavonoid content in flowers decreased with increasing precipitation but increased in fruits. Phenolic compounds in flowers decreased with altitude but increased with temperature.